This invention generally relates to electronic communications, and in particular, to a low power optically coupled serial data link which may be adapted for use with standardized communication protocol such as RS-232.
Power consumption in electronic communication equipment has become increasingly problematic in recent years with the proliferation of computerized devices and sensors. Industrial applications utilize a wide variety of xe2x80x9csmartxe2x80x9d devices, such as differential pressure transmitters, temperature sensors and other devices, which gather and transmit data to a centralized computer system. Often, these devices are located in geographically remote areas which makes access by maintenance personnel difficult and expensive. These devices are often battery or solar powered to enable them to communicate with the host computer. However, the communication circuits consume a great deal of power, requiring larger, heavier and/or more expensive batteries and solar panels in order to allow the equipment to function unattended for an extended length of time.
Moreover, many of these devices communicate over standardized protocols, such as RS-232 which tend to consume comparatively large amounts of power. Although more efficient communication circuits could be designed, they are impractical to use with conventional components since most vendors have built standardized interfaces into their equipment.
Moreover, all RS-232 signals are referenced to a common ground point, and because of this, connecting systems with different ground potential is difficult. More particularly, the common ground of the RS-232 interface introduces noise in the data channel, makes low level measurements difficult, and introduces susceptibility to damage from lightning generated surges. One solution to this has been the use of optical fiber and optical isolation circuits. However, this also increases the power consumption of both the transmitter and receiver portions of an RS-232 communication circuit. This in turn requires even larger, heavier and more costly batteries or solar panels.
Still a further problem with conventional RS-232 communication circuits is that the RS-232 interface specifies a maximum data rate of 50 feet at 19.2 KBaud. This transmission rate limitation becomes increasingly important as modem computer equipment attains increasingly higher processing speeds. To overcome this limitation, standard communication systems using the RS-232 specification either tend to keep the transmission rate below 19.2 KBaud, or include other transmission equipment, such as modems, between the RS-232 interface. In either event, power consumption and system costs are increased.
Accordingly, it is an object of the invention to provide an optical interface that consumes comparatively little power from its power source, yet is adaptable to standardized communication protocols. It is a further object of the invention to provide an optical serial interface that allows data transmission rates in excess of 19.2 KBaud using, for example, standard RS-232 protocol without consuming excessive amounts of power. It is still a further object of the invention to provide an optical data interface that allows for accurate measurement of low level signals, even in the presence of electromagnetic interference from alternating current equipment, while providing increased protection from electrical surges.
Other objects and advantages of the invention will become apparent in view of the following disclosure.